Fernandez and the former Jorge Bergoglio clashed so often that his official biographer, Sergio Rubin, compared them to "oil and water." When Bergoglio urged parishioners to join a campaign he called "God's war" against gay marriage, she compared the Argentine church leader's tone to the Middle Ages and the Inquisition. In 2010, Argentina became the first country in Latin America to legalize gay marriage.

But Wednesday night, her spokesman said there should be "no doubt" that Fernandez will travel to the Vatican to attend Francis' installation as pope next Tuesday.

In her open letter, she expressed to "your Holiness my consideration and respect."